Firstly preheat the oven to 180°C for 20 minutes. In a bowl add the softened butter and sugar and mix with a electric hand blender or with a spatula until soft, creamy, fluffy and pale in colour. By this process a lot of air wil incorporate and will help as a rising agent.
Now add sifted flour, custard powder and vanilla extract to the butter and sugar mixture.

At this stage mix it with spatula until combined into a smooth mixture. Make sure to use very thin edge spatula preferably steel one. Wash your hands and pat dry because you may have to use your hands to bring it together into a smooth dough. Make small 1 inch balls out of the dough. Place on a parchment lined baking tray. Press the dough balls on top with a fork to make impressions on it and flatten it slightly. Bake for 18-20 minutes. Do not let them brown.